Electrodes and nozzles having improved connection and quick release

ABSTRACT

Electrode and nozzle that seat within a retaining member and in two different seating locations relative to retaining member. The electrode and nozzle each include an interwoven-double-start thread having two thread cuts, which start 180 degrees from one another as measured around the circumference of the electrode or nozzle. Further, the electrode, nozzle, and retaining member include mating frustum surfaces, which are configured and dimensioned so that the electrode and nozzle seat within the retaining member with less than one turn of the electrode and nozzle relative to the retaining member. Therefore, the electrode and nozzle may be quickly inserted in, and removed from, the retaining member.

1. BACKGROUND OF THE INVENTION

[0001] A. Field of Invention

[0002] The present invention relates generally to a plasma torch and,more particularly, to a connection between a plasma torch electrode,nozzle, and a retaining member.

[0003] B. Description of the Related Art

[0004] Commonly used for working of metals, plasma arc torches are usedfor cutting, welding, surface treatment, melting, and annealing. Thesetorches include an electrode that supports an arc that extends from theelectrode to the workpiece in the transferred arc mode of operation. Itis also conventional to surround the arc with a swirling vortex of gas,and in some torch designs, it is conventional to envelope the gas andarc with a swirling jet of water.

[0005] It is known in the art of metal inert gas (mig) welding, that thewelding gun contact tip must satisfactorily perform two importantfunctions. First, it must accurately guide a weld wire to the point ofcontact with the work piece. Second, it must conduct adequate current,which can be as high as 400 amps or more, to the weld wire. To achievethose results, it is known to provide a relatively long contact tip madeof copper and having an axial hole therethrough. The hole is sizedslightly larger than the diameter of the weld wire. The contact tipextends from a gas diffuser through which an inert gas is directedaround the welding arc. Current to the contact tip is supplied to itthrough the gas diffuser.

[0006] Due to the severe operating conditions, contact tips haverelatively short service lives. Consequently, they are treated asconsumable items in the industry. Typically, contact tips are made asseparate pieces that are threaded into a gas diffuser. The thread is asingle thread and, therefore, each contact tip has only one seatinglocation with respect to the gas diffuser. When a contact tip has worn,it is threaded out of the gas diffuser, is discarded, and a new one isscrewed into its seating location.

[0007] As noted above, in addition to heating caused by the welding arc,another potential source of heat to the contact tip is the threadsbetween it and the gas diffuser. That is, the threads can causeresistance heating. To minimize electrical resistance, the contact tipand gas diffuser threads have a relatively long engagement length and afine pitch. However, the long engagement, fine pitch, thread presents aproblem. Removing a worn contact tip from the gas diffuser requiresseveral turns of the contact tip. If the weld wire has burned back andfused to the contact tip, the weld wire must twist through the samenumber of turns as the contact tip. The potential springback of thefully removed contact tip due to the twisted weld wire is annoying ifnot potentially dangerous. Moreover, the time required to disassemblethe multiple-turn contact tip also contributes to downtime of thewelding production area.

[0008] Although the prior art has individually addressed the problems ofshort service life of a contact tip, resistance heating, and quickreplacement of a contact tip, there has not been one convenientconfiguration that solves all of these problems.

[0009] U.S. Pat. No. 5,440,100 to Stuart et al. and U.S. Pat. No.3,469,070 to Bernard et al. each discloses a contact tip that can beseated in two different positions within a gas diffuser. Stuart andBernard use a projection on the gas diffuser, wherein the projectionfits into a groove on the contact tip. But such a connection is weakboth mechanically, and electrically. Mechanically, there is only a pointcontact between the gas diffuser and contact tip that holds themtogether. In Stuart, a dimple or protrusion extends from the gasdiffuser; however, the dimple is subject to wear each time a contact tipis inserted within the gas diffuser thereby making the mechanicalconnection loose over time. In Bernard, a set screw in the gas diffuserextends into a bore that receives the contact tip. The tip of the setscrew fits into recessed guideways on the contact tip. But the set screwmay loosen due to vibration during use of the welding gun and,therefore, weaken the mechanical connection between the contact tip andgas diffuser. Further, the point contact tends to loosen easily therebyallowing the contact tip to rattle within, and quite possibly come outof, the gas diffuser, which would be a big problem during weldingoperations. Electrically, each Stuart and Bernard suffers the drawbackof resistance heating near the limited point contact between theprojection and the groove that hold the parts together.

[0010] U.S. Pat. No. 5,760,373 to Colling addresses the problem ofresistance heating by providing a welding device having a taperedconnection between a contact tip and a gas diffuser. However, Collingstill suffers the drawback of requiring a full turn of the contact tipto remove or insert it within the gas diffuser. Moreover, Colling'scontact tip seats in only one position relative to the gas diffuser and,therefore, suffers the additional drawback of a short service life.

[0011] Similarly to Colling, U.S. Pat. No. 5,726,420 to Lajoie providesa welding device having a tapered connection between a contact tip and agas diffuser. Lajoie claims to enable quick replacement of the contacttip, however, Lajoie's device requires 2½ turns of the contact tiprelative to the gas diffuser in order to remove or insert it. Lajoie'srequired 2½ turns is still quite time consuming and, therefore,contributes to a long downtime during replacement of the contact tip.Further, Lajoie's electrode seats in only one position relative to thegas diffuser and, therefore, suffers the additional drawback of a shortservice life.

[0012] U.S. Pat. No. 5,023,425 (Severance, Jr.) which issued on Jun. 11,1991, and which is incorporated herein by reference, discloses anelectrode for a plasma arc torch wherein the electrode includes a copperholder having a lower end that mounts an emissive insert that acts asthe cathode terminal for the arc during operation.

II. SUMMARY OF THE INVENTION

[0013] It is an object of the present invention to overcome thedisadvantages of the prior art by providing a plasma apparatusconfiguration that solves the problems of short service life, resistanceheating, and quick replacement of the plasma tip, with one simpledesign. It is another object of the invention to provide a plasmaapparatus with a plasma electrode and plasma tips that have longerservice lives than conventional plasma electrodes and plasma tips,thereby reducing the cost of operating the plasma apparatus. Further, itis an object of the present invention to provide a plasma apparatus inwhich plasma electrodes, plasma tips, and a plasma torch quickly may beconnected and disconnected, thereby reducing the time necessary forreplacement of the plasma electrode and plasma tip and thus decreasingdown-time of a plasma production area. Further, although the plasmaelectrode and plasma tip may be quickly removed and inserted within theplasma torch, the present invention provides a strong connectiontherebetween, which also minimizes resistance heating.

[0014] In accordance with the present invention, a plasma apparatus isprovided with a plasma electrode and plasma tip having a longer servicelife. In order to provide longer service life, the plasma electrode andplasma tip have an interwoven-double-start thread, wherein thethread-cut starting points are 180 degrees from one another.Additionally, the plasma torch has a plasma electrode- and plasmatip-mating thread which is also an interwoven-double-start thread,wherein the thread-cut starting points are 180 degrees from one another.By providing an interwoven-double-start thread on the plasma electrode,plasma tip, and the plasma torch, the plasma electrode and plasma tipmay be seated in two positions, 180 degrees apart from one another,relative to the plasma torch.

[0015] Additionally, in accordance with the present invention, a quickrelease plasma electrode and plasma tip are provided that minimizeresistance heating between the plasma electrode, plasma tip, and plasmatorch. The plasma electrode, plasma tip, and plasma torch are designedto seat with less than one turn of the plasma electrode and plasma tiprelative to the plasma torch, thereby reducing the time necessary tochange a plasma electrode and plasma tip. Even though the plasmaelectrode and plasma tip seat with less than one turn, the connectionbetween them and a plasma torch is strong because of theinterwoven-double-start threads. The interwoven-double-start threads, onthe plasma electrode, plasma tip, and plasma torch, provide a longereffective thread length—over less than one turn—as opposed to theconventional single thread. The longer effective thread lengthstrengthens the connection as well as reduces resistance heating. Thus,the interwoven double-start threads reduce the resistance heating andincrease connection strength while minimizing the number of turnsrequired to seat the plasma electrode and plasma tip in the plasmatorch. To further strengthen the connection between the plasmaelectrode, plasma tip, and plasma torch, as well as to reduce resistanceheating, the plasma electrode, plasma tip, and plasma torch have matingfrustum surfaces.

[0016] The upstream end of the plasma torch may be constructed to suitany desired plasma system. The various ports and passages for the gasesmay also take any desired shape. The downstream end of the plasma torchis provided with a frustum-shaped cavity having its apex end toward theplasma torch upstream end. The base of the frustum-shaped cavityterminates in an interwoven-double-start thread that terminates at thedownstream edge of the plasma torch.

[0017] The downstream ends of the plasma electrode and plasma tip may beconventional.

[0018] With the plasma electrode and plasma tip assembled to the plasmatorch, the entire area of the plasma electrode's and plasma tip'sfrustum is in intimate facing contact with the plasma torch'sfrustum-shaped cavity. In addition, the engaged areas of the interwovendouble-start threads of the two parts are in contact. The large areas ofcontact between the two parts provide a strong connection, as well asenable them to handle heavy current with minimized resistance heating.Further, quick replacement is possible because less than one reverseturn of the plasma electrode and plasma tip is required to remove itfrom, and insert it into, the plasma torch.

[0019] Still other benefits and advantages of the invention will becomeapparent to those skilled in the art to which it pertains upon a readingand understanding of the following detailed specification.

III. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention may take physical form in certain parts andarrangement of parts, a preferred embodiment of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof and wherein:

[0021]FIG. 1 is a sectional side view of a plasma arc torch, whichembodies the features of the present invention.

[0022]FIG. 2 is an exploded perspective view of a plasma torch body,electrode, and nozzle according to the present invention.

[0023]FIG. 3 is a schematic diagram of an interwoven-double-startthread, as is on the torch body, electrode, and nozzle of the presentinvention.

IV. DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] Referring now to the drawings wherein the showings are forpurposes of illustrating a preferred embodiment of the invention onlyand not for purposes of limiting the same, FIG. 1 shows a plasma arctorch. The plasma arc torch 10 includes a nozzle 12 and an electrode 14.The electrode 14 is made preferably of copper or a copper alloy.

[0025] In accordance with the present invention, the torch body 16 andelectrode 14 are designed so that the electrode 14 can be seated, andused, in two different positions relative to the torch body 16. Further,the torch body 16 and electrode 14 are designed to provide a quickrelease, yet strong connection, therebetween while conducting maximumcurrent to the work piece. In the embodiment shown in FIG. 2, the torchbody 16 is generally tubular in shape, having an upstream end 11, adownstream end 17, and an axial passage 13. A first internalinterwoven-double-start thread 18 is machined into the inside of thetorch body 16 near the downstream end 17 of the axial passage 13. Asecond internal interwoven-double-start thread 19 is machined into thedownstream end 17 of the axial passage 13.

[0026] The electrode 14 has an upstream end 21 and a downstream end 27.An external interwoven-double-start thread 24 is machined into theupstream end 21 of the electrode 14. The interwoven double-start thread24 has the same diameter and pitch as the first interwoven-double-startthread 18 in the torch body 16.

[0027] A working end 25 of the electrode 14 extends from theinterwoven-double-start thread 24 to the downstream end 27. The workingend 25 may have a cylindrical surface, as shown, or any other suitableshape as, for example, that of a frustum, or combination of cylindricalsurface and frustum. Additionally, the working end 25 may have apolygonal cross section. Further, when the working end 25 does notinclude a cross section having flat surfaces, it may be provided withwrench flats 28 to assist in turning the electrode 14 relative to thetorch body 16.

[0028] The nozzle 12 has an upstream end 31 and a downstream end 37. Aninside hole 36 extends axially through the interior of the nozzle 12over its entire length. An external interwoven-double-start thread 34 ismachined into the upstream end of the nozzle. The interwovendouble-start thread 34 has the same diameter and pitch as the secondinterwoven-double-start thread 19 in the torch body 16.

[0029] A schematic diagram of an interwoven-double-start thread is shownin FIG. 3. The schematic diagram is representative of each of theinterwoven-double-start threads 18, 19 on the torch body, theinterwoven-double-start thread 24 on the electrode, and theinterwoven-double-start thread 34 on the nozzle. That is, theinterwoven-double-start threads 18, 19, 24, 34 are similar because theycorrespond to, and mate with, one another. As shown in FIG. 3, theinterwoven-double-start thread pattern includes two thread cuts T1 andT2. The thread cuts T1 and T2 start in the same plane, but 180 degreesfrom one another, as measured around the circumference of the part onwhich they are located. Further, the turns of one thread cut, T1 forexample, are disposed between adjacent turns of the other thread cut T2.That is, the thread cuts T1 and T2 alternate along an axial lineextending parallel to the longitudinal axis of the part on which theyare located. The interwoven-double-start threads 18, 19 include threadcuts that are similar to the schematic thread cuts T1 and T2,respectively, of FIG. 3. Similarly, the interwoven-double-start threads24, 34 include thread cuts that are similar to the schematic thread cutsT1 and T2, respectively, of FIG. 3. The thread cuts are designed so thatthe interwoven-double-start threads 18, 19 in the torch body mate withthe interwoven-double-start threads 24, 34 on the electrode and nozzlerespectively.

[0030] The torch body 16 and the electrode 14 are used by screwing theinternal threads 18 of the torch body to the corresponding threads onthe electrode 14. The electrode 14 is inserted into the downstream end17 of the torch body until the electrode interwoven-double-start thread24 contacts the torch body interwoven-double-start thread 18. Theelectrode 14 is then turned until the interwoven-double-start threads18, 24 engage. The electrode 14 is further turned until the end 21 comesinto contact with the torch body 16, as shown in FIG. 2, therebyconnecting the electrode 14 to the torch body 16 in a first seatinglocation. The interwoven-double-start threads 18, 24, are configured anddimensioned so that the electrode 14 mates with the torch body 16 afterless than one turn of the electrode 14, after theirinterwoven-double-start threads 18, 24 have initially engaged, andbefore the electrode interwoven-double-start thread 24 has reached theend of the torch body interwoven-double-start thread 18. The sameinterrelationship applies to the torch body and the nozzle.

[0031] When it is necessary to remove an electrode 14 or a nozzle 12,less than one reverse turn is sufficient to release each from the torchbody 16. Similarly, a new electrode 14 is assembled to the torch body 16with less than one turn. Similarly, a new nozzle 12 is assembled to thetorch body 16 with less than one turn. The entire replacement process isaccomplished with very little downtime.

[0032] Moreover, although the electrode 14 is rotated less than one turnbefore seating within the torch body 16, there is a large area ofcontact therebetween. The interwoven-double-start threads 18, 24 contactone another. The large contact area provides the electrode 14 with astrong seat in the torch body 16. Additionally, when the electrode 14 isseated within the torch body 16, a considerable current can be conductedto the work piece by the torch body 16 and electrode 14 because of thelarge area of contact between the two parts. Consequently, resistanceheating in and between the parts during operation of the plasma torch 10is minimal.

[0033] It is contemplated that numerous modifications may be made to theplasma welding device of the present invention without departing fromthe spirit and scope of the invention as defined in the followingclaims. For example, an electrode and torch body could, of course, havean interwoven-double-start thread whereas another electrode and torchbody could then include a single thread having a pitch corresponding toone thread cut of the interwoven-double-start thread. With such anarrangement, the electrode would still be able to seat in two differentlocations with respect to the torch body thereby extending the servicelife of the electrode.

[0034] The remaining plasma arc torch structure is conventional and isdisclosed in the '425 patent mentioned above, which is incorporatedherein by reference.

[0035] A power supply P, not shown, is connected to the torch electrode14 in a series circuit relationship with a metal work piece, which istypically grounded. In operation, the plasma arc is established betweenthe electrode 14 of the torch 10, which acts as the cathode terminal forthe arc, and the work piece which is connected to the anode of the powersupply, and which is positioned below the nozzle 12. The plasma arc isstarted in a conventional manner by momentarily establishing a pilot arcbetween the electrode 14 and the nozzle 12.

[0036] The preferred embodiments have been described, hereinabove.. Itwill be apparent to those skilled in the art that the above methods mayincorporate changes and modifications without departing from the generalscope of this invention. It is intended to include all suchmodifications and alterations in so far as they come within the scope ofthe appended claims or the equivalents thereof.

Having thus described the invention, it is now claimed:
 1. An electrodefor supporting an arc in a plasma arc torch comprising: a body having afirst end, a second end, and a longitudinal axis, wherein the first endis opposite to the second end along the longitudinal axis, wherein thefirst end of the body includes an interwoven-double-start thread, andwherein the interwoven-double-start thread includes two thread cuts,each of the two thread cuts having a transverse profile with a base thattapers to a flat crest.
 2. An electrode as claimed in claim 1, whereinthe interwoven-double-start thread comprises two thread cuts that startat positions that are 180 degrees from one another as measured aroundthe circumference of the body.
 3. An electrode as claimed in claim 1,wherein the interwoven-double-start thread comprises a first thread cutand a second thread cut which are interwoven so that the first threadcut alternates with the second thread cut along a line parallel to thebody longitudinal axis.
 4. (Cancelled)
 5. (Cancelled)
 6. (Cancelled) 7.(Cancelled)
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 10. (Cancelled) 11.(Cancelled)
 12. (Cancelled)